Disposable absorbent article with unitary topsheet and unitary absorbent article

ABSTRACT

The present invention relates to disposable absorbent articles such as sanitary napkins, panty liners, baby diapers, adult incontinence articles and sweat pads. According to the present invention the absorbent article in the region designated for liquid deposition on its wearer facing surface has a single layer topsheet onto which liquid to be absorbed is provided during use of the article. The absorbent article includes a backsheet forming the liquid barrier surface and a unitary absorbent core between the topsheet and the backsheet. Importantly the unitary core provides improved liquid handling to the absorbent article and increases the masking, i.e. ability to hide stains due to absorbed liquid, of the article. This is particularly beneficial in the context of articles for absorption of liquids with high color intensity, such as menstrual liquid or urine of older adults.

FIELD OF THE INVENTION

The present invention relates to disposable absorbent articles such assanitary napkins, panty liners, baby diapers, adult incontinencearticles and sweat pads. According to the present invention theabsorbent article in the region designated for liquid deposition on itswearer facing surface has a single layer topsheet onto which liquid tobe absorbed is provided during use of the article. The absorbent articlefurther comprises a backsheet forming the liquid barrier surface and aunitary absorbent core between the topsheet and the backsheet.Importantly the unitary core provides improved liquid handling to theabsorbent article and increases the masking, i.e. ability to hide stainsdue to absorbed liquid, of the article. This is particularly beneficialin the context of articles for absorption of liquids with high colorintensity, such as menstrual liquid or urine of older adults.

BACKGROUND OF THE INVENTION

Absorbent articles are well known in the art. Particularly sanitarynapkins of all kinds of designs are well documented. Although the use ofunitary cores is known in the art of disposable absorbent articles andhas been disclosed previously such articles have not been successful ortechnically satisfactory as evidenced by the lack of commerciallyavailable embodiments.

The word “unitary” as used herein refers to a single structure, whichdespite potential internal variations of physical and/or chemicalcharacteristics is provided such that it cannot be separated intoindividual layers. Such unitary structures are well known in the art andoften referred to also as substrates. However, absorbent cores indisposable absorbent articles have been provided from a number of layersor associated with a multi-layer structure as the topsheet. In thiscontext it is pointed out that a construction in which a topsheet with asecond underlying layer, (at least in the region where liquid is usuallydeposited onto the article), referred to as secondary topsheet ordistribution layer, is provided on top of a unitary absorbent structure,is excluded from the definition of the absorbent articles according tothe present invention. Also structures made from a number of layers,which are joined to each other by macroscopic mechanical or adhesivemeans, are well know and not uncommon in the practical embodiments ofabsorbent articles available to consumers. Such structures, however, arealso not considered unitary in the sense of the present invention sincethey are formed from individual layers that, albeit sometimes withdifficulty, can be separated from each other again.

A unitary fluid acquisition, storage and wicking material is disclosedfor example in WO 0074620 in which fibrous absorbent structures havingseparate strata or thickness regions for fluid acquisition storage anddistribution are disclosed.

This disclosure, however, suffers from the design of an acquisition,storage and distribution layer system, which simply resembles thedesigns obtainable by a combination of layers. The fact that theselayers are laid down in a single process, preferably as an air laidprocess, does not change the deficiencies originally found in themulti-layered constructions widely used in commercial article with theexception that the liquid communication between the layers is improved.The present application, however, also improves the ability of suchunitary structures to mask stains visible on the topsheet side of anabsorbent article, besides providing excellent liquid communicationcharacteristics between the differing layers or strata.

The present invention also is particularly directed to the absorbentarticle employing unitary absorbent cores in such a way that noadditional layers between the unitary topsheet and the unitary absorbentcore is provided at least in the region where liquid is deposited duringusual use. It is therefore an advantage of the present invention that alay down of three layers, a topsheet, a unitary absorbent core and abacksheet is capable of providing the full and improved functionality ofabsorbent articles and thereby reduces manufacturing complexity for sucharticles. Within the various aspects of manufacturing complexity itshould be noted that the simplification in raw material procurement, rawmaterial delivery to a production facility and simplification ofcombining the raw materials to a finished absorbent article is muchsimplified with the absorbent article design according to the presentinvention.

SUMMARY OF THE INVENTION

According to the present invention a disposable absorbent article suchas a sanitary napkin having a wearer facing surface and a garment facingsurface is provided which article comprises a topsheet, a backsheet(preferably joined to the topsheet), and an absorbent core interposedbetween the topsheet and the backsheet. Each of the components,topsheet, backsheet, and absorbent core, has a wearer-facing surface anda garment-facing surface.

The disposable absorbent article has a liquid deposition region in whichduring conventional use of the article, liquids are deposited forabsorption in the article.

The topsheet forms the outermost surface and the wearer-facing surfaceof the absorbent article. The liquid pervious topsheet consists of asingle layer at least in the liquid deposition region. The backsheetforms the liquid barrier surface and the garment-facing surface of thearticle. The absorbent core is intermediate the topsheet and thebacksheet. The absorbent core is unitary and has a wearer facing and agarment-facing surface. The garment-facing surface of the core isimmediately adjacent, (that is in direct liquid contact with) thebacksheet and the wearer-facing surface of the absorbent core isimmediately adjacent to the topsheet.

The unitary core is provided as a fibrous stratified layer structurewith at least three layers. All layers are unified into a unitary coreby a single thermal combining step or by a single felting step or by acombination of both a thermal combining and a felting step. There is noadhesive used between the layers of the absorbent core, as this is notnecessary due to the unitary construction and the combining beingconducted on the layers in a single step.

The at least three layers of the absorbent core comprise a firstoutermost layer forming the wearer-facing surface of a core. The firstlayer is provided as a mixture of bi-component fibers and cellulose orviscose fibers, but preferably non-softened cellulose fibers thattogether provide an overall weight fraction of the absorbent core or10%-30%. The core has a second outermost layer, which forms thegarment-facing surface of the core. The second layer of the core isprovided by softener treated cellulose fibers. This layer of the coreprovides an overall weight fraction of a core of 30%-50% and optionallycomprises a surface binder, preferably latex, as a dust control means,which is applied onto the garment-facing surface of the core in anamount of 0%-2% by weight of the core.

Finally, the absorbent core has at least one inner layer, which issandwiched between the first and the second layer. This inner layercomprises non-softened cellulose fibers, optionally a bi-componentfiber, preferably mixed homogeneously with the non-softened cellulosefibers. The inner layer further comprises a super-absorbent material,preferably in particulate form. The inner layer has a weight fraction ofthe overall core between 30% and 50% of the core. The disposableabsorbent article is particularly characterized in that the unitary coreis free of binder material, except for the bi-component fibers in thelayers of the core and the optional surface binder on the garment-facingsurface of the core.

In a preferred embodiment the surface binder for dust control is notrequired in the absorbent core. In a further preferred embodimentaccording to the present invention, the first layer of the absorbentcore comprises between 60% and 95% by weight of the bi-component fibersand 5%-40% by weight of cellulose or viscose fibers. Preferably thebi-component fibers have a cross section with a polypropylene centralportion and a polyethylene outer coating around the polypropylene. Morepreferable and resulting in a curled bi-component fiber is if thepolypropylene central portion is not symmetrical in respect to thecenter point of the cross section of the bi-component fibers. Thisresults in curling of the bi-component fibers providing extra resiliencyat least to the first layer of the absorbent core.

In a yet alternative preferred embodiment the bi-component fibers of theinner layer of the absorbent core has a large diameter by having acoarseness of at least 10 dtex, preferably between 12 dtex and 20 dtexand more preferably between 15 dtex and 18 dtex. Finally, for ease ofmanufacturing and without sacrifice of performance of the absorbentarticle according to the present invention, a highly preferredembodiment will use only one kind of bi-component fibers in accordancewith the above-preferred designs.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic cross section of a sanitary napkin showing theinternal layered structure of a sanitary napkin according to a preferredembodiment of the present invention.

FIG. 2 shows an enlarged portion II of the absorbent structure of thenapkin of FIG. 1 including a schematic view of the transition betweentwo layers in the core.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to absorbent disposable articles such assanitary napkins, panty liners, incontinence product, sweat pads, andbaby diapers. Typically such products comprise the elements of a liquidpervious topsheet, a backsheet and an absorbent core intermediate saidtopsheet and said backsheet. According to the present invention, thetopsheet, backsheet, and core may be selected from any of the knowntypes of these components provided that they meet the design andmaterial criteria and conditions noted below and in the appended claims.

In general, the topsheet should have good liquid retention to maintain adry surface and thereby keep the skin of the wearer dry; the absorbentcore needs to provide enough absorbent capacity and preferably allowsthe flow of vapor and/or air through it and the backsheet should preventwet through (liquid impermeability) to retain the absorbed fluid whilepreferably being sufficiently breathable. Furthermore, the individualelements are joined to each other, preferably using techniques such thatthe final product has the desired comfort and performance level.

In the following description of the invention the surface facing in thedirection of the wearer is called wearer-facing surface. In the drawingthis direction is towards the top of the page. Further the surfacefacing in the direction of the garment is called a garment-facingsurface and in the drawing this direction is towards the bottom of thepage.

In the following description the term “a liquid deposition region” ofthe article is used. The liquid deposition region is that region of thearticle where in usual use liquid is predominantly deposited. The regionhence depends in its exact dimension and location on the article. Theskilled person will however know or be able to define the minimumdimension and location of the liquid deposition region. In particularfor feminine care articles, i.e. napkins or panty liners, this region iscentrally located having a 2-5 cm minimum width and 3-12 cm minimumlength.

Absorbent Article Components The Topsheet

According to the present invention the absorbent article comprises aliquid pervious topsheet. The topsheet suitable for use herein comprisewovens, non-wovens, and three-dimensional webs of a liquid impermeablepolymeric film comprising liquid permeable apertures. In FIG. 1 thetopsheet is indicated with reference numeral 30.

The topsheet for use herein is a single layer at least in the liquiddeposition region but may have a multiplicity of layers (31) outside ofthe liquid deposition region. In a preferred embodiment the topsheetacross its full extension is a single layer, which provides theuser-facing surface of the topsheet in the liquid deposition region andthe garment-facing surface of the topsheet. Optionally on the wearerfacing surface of the topsheet but only extending in the peripheral zoneof the article an additional layer can be desirable to provide extrasoftness or extra liquid handling/retaining abilities (this design isusually referred to as “hybrid topsheet”). The topsheet typicallyextends across the whole of the absorbent structure and can extend intoand form part of or all of the preferred but optional side flaps,side-wrapping elements, wings or ears. Also the topsheet can wrap aroundthe absorbent core edges. Fundamentally the topsheet can be provided asa single layer, which for simplicity of manufacturing is the preferreddesign.

The topsheet as a whole needs to be compliant, soft feeling, andnon-irritating to the wearer's skin. It also can have elasticcharacteristics allowing it to be stretched in one or two directions.The topsheet has the principle function of acquisition and transport offluid from the wearer towards the absorbent core and containment of theabsorbent core.

In addition to liquid permeability the topsheet should have a high vaporpermeability and/or air permeability.

According to the present invention the topsheet can comprise woven,non-wovens, but preferably a liquid permeable apertured polymeric film,preferably the wearer facing and contacting surface at least in theliquid deposition region, is provided by a film material havingapertures which are provided to facilitate liquid transport from thewearer facing surface towards the absorbent structure. Such liquidpermeable, apertured films are well known in the art. They provide aresilient three-dimensional fiber-like structure. Such films have beendisclosed in detail for example in U.S. Pat. No. 3,929,135, U.S. Pat.No. 4,151,240, U.S. Pat. No. 4,319,868, U.S. Pat. No. 4,324,426, U.S.Pat. No. 4,343,314, U.S. Pat. No. 4,591,523, U.S. Pat. No. 4,609,518,U.S. Pat. No. 4,629,643, U.S. Pat. No. 4,695,422 or WO 96/00548.

An example of such film is available from the Procter & Gamble Company,Cincinnati, Ohio, USA under the trade name Dry weave. Also such filmsare available from the Company Pantex from Pistoia, Italy under thedesignation “PF-films”. Also film according to U.S. Pat. No. 5,591,510or WO 97/03118 and WO 97/03795 described for use as a layer inbreathable backsheet can be employed but may require modification of theapertures to ensure liquid permeability from the wearer-facing surfaceto the absorbent core that is the primary objective of the topsheet.Such modification can e.g. be a surface energy alteration that activelydrives liquids into and through apertures by creating a gradient ofsurface tension of the film. A method to provide surface energygradients is disclosed e.g. in WO 96/00548.

Absorbent Core

According to the present invention, the absorbent cores suitable for useherein are unitary. In FIG. 1 the absorbent core is shown as a singlelayer 40 constituted by sub-layers or strata 41, 42, 43, 44.

The absorbent core of the present invention should have high vaporpermeability preferably also high air permeability. The absorbent corepreferably has a caliper or thickness of less than 12 mm, preferablyless than 8 mm, more preferably less than 5 mm, most preferably from 4mm to 2 mm.

According to the present invention, the absorbent core includes thefollowing sub-layers: (a) a first outermost layer 41 providing thesurface adjacent the topsheet 30 optionally together with anintermediate layer 42; (b) a fluid storage layer 43; (c) a secondoutermost layer 44 providing the surface adjacent the backsheet.

First Layer

One component of the absorbent core according to the present inventionis a first layer. The first layer underlies the topsheet and is indirect fluid communication therewith. The topsheet transfers theacquired fluid to this first layer for ultimate distribution to thestorage layer. This transfer of fluid through the primary distributionlayer occurs primarily but not only in the thickness, but also along thelength and width directions of the absorbent product.

The first layer forms the wearer-facing surface of the absorbent coreand is hence a layer of an outermost surface of the core. The firstlayer is provided from mixtures of fibers. The mixture of fibersconsists of bi-component fibers and hydrophobic fibers as cellulosesand/or viscose fibers, preferably non-softened cellulose fibers.Preferably the mixture is selected such that 60%-95% by weight of thefirst layer is provided by bi-component fibers and 5%-40% by weight isprovided by cellulose and/or viscose fibers. Of course, a mixture of(non-treated) cellulose and viscose fibers may also be chosen, as theseare considered equivalent. In a preferred embodiment the amounts will beeven stricter selected to be 80%-90% by weight of the bi-componentfibers and 10%-20% by weight of (non-treated) cellulose or viscosefibers.

As used hereinafter the term bi-component fibers refers to fibers havingtwo constituents. Typically bi-component fibers are constituted ofrelatively similar constituents, which are differing, for example intheir melting temperature or softening temperature. Particularembodiments and preferred in the context of the present invention arepolypropylene/polyethylene bi-component fibers but other combinationssuch as polyester/polyethylene, polyester/polypropylene,polyamide/polyester, polyamide/polyethylene, polyamide/polypropylene arealso feasible combinations. The conventionally used material is,however, the above-mentioned polypropylene polyethylene fibercomposition which is provided in a form such that in a cross-sectionalview of a fiber the material with the higher melting or softening pointprovides the central part or the core of the fiber and typically isresponsible for the fiber ability to transmit forces and have a certainrigidity or provide structures with resiliency while the outer coatingon the core of the fiber has a lower melting point and is used tofacilitate thermally bonding of substrates comprising such fibers. It isparticularly preferred if the so-called shaft core design ofbi-component fibers is not exactly point-symmetrical to the centralpoint of the cross section but provides the shaft part of the fiber inan asymmetric form so that the fiber is caused to curl. This has beenfound to provide a beneficial effect on resiliency and strength of thefiber.

In a typical embodiment according to the present invention, apolypropylene core is provided with a polyethylene coating on theoutside in an asymmetric form such that in a highly preferredembodiment, in about 50% of the fiber material is polypropylene and 50%of the fiber material is polyethylene. Other quantitative amounts can ofcourse be selected and will strongly depend on the overall fiberdimensions as the binder quantity of the surface of the fiber providedpreferably by the polyethylene needs to have a certain thickness inabsolute terms for the provision of good bonding while its relativequantity can vary. According to the present invention very thick fiberscan be used and it has been found that bi-component fibers of thepolyethylene polypropylene kind, but also other material compositions asindicated above, are preferably provided in a coarseness of at least 10dtex, preferably between 12 dtex and 20 dtex and more preferably between15 dtex and 18 dtex. An example of such bi-component fibers is availablefrom the company ES Fibervision, Engdraget 22, DK-6800 Varde, Denmark,under the trade name ES-Delta having 16.7 dtex and being provided by apolypropylene core and fully coated by polyethylene. These fibers areavailable in carded form, having a length of approximately 4.6 mm, whichhave been found useful in the context of the present invention. Anexample of fine bi-component fibers, usable in the present inventionespecially in the first layer are A1 Adhesion 1.7 dtex also from thecompany Fibervsion.

The other fiber used in the context of the present invention in thefirst layer is the fiber of (non-treated) cellulose or viscose/rayonfibers or combinations thereof. The term “treated” in this contexttypically refers to softening treatment and both terms are usedsynonymously herein. Such fibers are widely available and are made inthe context of manufacturing of paper. These fibers historically havebeen well-known and both versions, the more brittle and less flexiblenon-softened cellulose fibers, which have simply not undergone atreatment with a softening material, such as for example a quaternaryammonium material, well-known in the art of paper making, are used inthe layer to reinforce this particular resiliency desirable for thisfirst layer. This provides exceptional capability of allowing liquid tobe acquired without collapsing under its own weight. Particularlypreferred and used in an embodiment according to the present inventionis the use of viscose/rayon fibers in this first layer at an amount ofabout 15%. Such viscose/rayon fibers are available from a large numberof commercial sources. The remainder of the first layer structure wasprovided by the above-mentioned fibers provided by Fibervision (Supra).

As can be seen from the drawing FIG. 1, the first layer 41 is followedby a second layer (42) indicated by small dots implying that this is aparticularly thin layer of purely bi-component fibers or low meltingpoint thermoplastic fibers such as polyethylene fibers, providingespecially good thermo integration with the following layer (43).

In a separate consideration, this layer could also be provided by anextremely fine mix of adhesive fibers that are sprayed in the course ofmanufacturing of the unitary core according to the present invention. Asthe present invention as defined in the claims does not include suchdesign due to the use of adhesive, it is here only mentioned as apotential alternative, which, in case of search for an alternative tothe present invention, could be useful with minor sacrifice of some ofthe beneficial characteristics of the present invention. It is evenconceivable to combine the first layer with the remainder of the unitarycore structure by such a mix of adhesive fibers after having integratedi.e. bonded the first layer and/or the remainder of the unitary corelayers prior to this binding. This not being preferred in accordancewith the present invention as claimed, nevertheless it is a possibilitythat for the sake of completeness should be mentioned in this context.

However, for the particularly beneficial embodiments according to thepresent invention, which in accordance with claim 1 as filed do notrequire any adhesive material layer (42) could also be provided bythermoplastic particles such as polyethylene powder. One preferredembodiment according to the present invention will simply not have alayer (42) in order to limit the structure to its most simple form(thereby simplifying the manufacturing process of the unitary core) to athree-layer structure.

Fluid Storage Layer

Positioned in fluid communication with, and typically underlying thefirst layer, is a fluid storage layer (43). The fluid storage layercomprises absorbent gelling materials usually referred to as “hydrogel”, “super-absorbent”, hydrocolloid” materials in combination withsuitable carriers.

The absorbent gelling materials are capable of absorbing largequantities of aqueous body fluids, and are further capable of retainingsuch absorbed fluids under moderate pressures. The absorbent gellingmaterials can be dispersed homogeneously or non-homogeneously in asuitable carrier but is preferably dispersed homogeneously.

Suitable absorbent gelling materials for use herein will most oftencomprise particles of a substantially water-insoluble, slightlycross-linked, partially neutralized, polymeric gelling material. Thismaterial forms a hydro gel upon contact with water such polymermaterials can be prepared from polymerizable, unsaturated,acid-containing monomers, which are well known in the art.

Suitable carriers include materials, which are conventionally utilizedin absorbent structures such as natural, modified or synthetic fibers,particularly non-softened cellulose fibers (in the form or fluff) orcombination thereof. However especially non-treated cellulose availablee.g. from the Weyerhauser company are used in the fluid storage layeraccording to the present invention.

A small amount of less than 50% weight of synthetic fibers can inaddition also be used and include those made of cellulose acetate,polyvinyl fluoride, polyvinylidene chloride, acrylics (such as Orlon),polyvinyl acetate, non-soluble polyvinyl alcohol, polyethylene,polypropylene, polyamides (such as nylon), polyesters, bi-componentfibers, tricomponent fibers, fibers with surface capillaries, mixturesthereof and the like. Preferably, the fiber surfaces of such fibers arehydrophilic or are treated to be hydrophilic. The storage layer can alsoinclude filler materials, such as Perlite, diatomaceous earth,Vermiculite, etc., to improve liquid retention. Preferred is the use ofa minor amount of bi-component fibers of the same kind used in the firstlayer.

If the absorbent gelling material is dispersed non-homogeneously in acarrier, the storage layer can nevertheless be locally homogenous, i.e.have a distribution gradient in one or several directions within thedimensions of the storage layer. Non-homogeneous distribution preferablyis used to leave portions of the entire periphery of the fluid storagelayer free of absorbent gelling material or at least with reducedamounts.

In an example of the fluid storage layer according to the presentinvention a mixture of 30% by weight of the layer is absorbent gellingmaterial, 60% by weight of the layer is provided by non-softenedcellulose fibers and 10% are bi-component fibers of the same kind usedin the first layer.

Second Layer

The second outermost layer for inclusion in the absorbent core accordingto the present invention is a fibrous layer 44 adjacent to, andtypically underlying the storage layer. This underlying fibrous layer orsecond outermost layer forms the garment-facing surface of the absorbentunitary core. The second layers provided by softener treated cellulosefibers providing this cellulose with a particularly good wetting surfaceand a reduced resiliency, thereby creating a denser cushioning effect inthat layer of the absorbent structure farthest away from the wearerduring use of the article. This layer should provide 30-50% of theoverall weight of the absorbent structure and should be providedexclusively by softener treated cellulose fibers or viscose fibers or acombination thereof. It is, however, due to the large amount of shortfibers found in such softener treated cellulose fluff materials possibleto provide the outermost surface, i.e. the garment facing surface ofthis layer with a minor amount of binder material sprayed or otherwisedistributed onto the outermost surface of this layer. This bindermaterial is not intended nor does it support binding of the overallabsorbent core but only provides a reduced dustiness and broken fiberdeparture from the surface of the second layer. In particular this mayonly be a manufacturing process related application of binder materialfor dust control rather than intended to affect the absorbent coreperformance aspects. The amount of such binder can be between 0% and 2%,preferably between 1% and 0% by weight of the absorbent core and ofcourse preferably left away if the dust control can be achieved bydifferent means during manufacturing of such articles. Binders can bee.g. latex type binders but simply using water has also been foundpossible.

Other Optional Components of the Absorbent Structure

The absorbent core according to the present invention can include otheroptional components normally present in absorbent webs. For exampleclose to or as part of the first layer or the fluid storage layer odorcontrol agents such as zeolites, carbon black, silicates, EDTA or othergelatins can be provided. Such agents are preferably provided inparticulate form or as part of particles and can be provided for exampletogether with the absorbent gelling material mentioned supra.

Integration of Layers in Unitary Core

According to the present invention, the unitary core is provided as asingle unitary structure. Thermo bonding or felting or combinations ofthese combining steps create it. Hence, the unitary core before anybonding can take place, needs to be provided by laying the variousmaterials described above onto each other, then a calendaring will takeplace in order to reduce the thickness and bulkiness of the structure.The calendaring step creates a densification, which provides the sameforce throughout the whole of the structure. This calendaring is thenfollowed by the thermo bonding or felting with needles or a combinationsuch as felting with hot needles and a hot air exposure of the unitaryabsorbent core structure.

It should be particularly noted that calendaring needs not be providedin a single step, it could be provided in two or more steps. Howeverimportantly the calendaring is conducted on the unitary structure as awhole, not on the individual layers.

Before the bonding between the layers, there is no particular integritywithin and between the layers of the core such that forces within theabsorbent structure are not supportable by the absorbent structure priorto bonding. Hence, the calendaring needs to take place very carefullyand will create already a minor mechanical integration between thevarious layers.

Interestingly it has been found that provided the above-mentioned designcriteria are followed, the compression will result in a higherdensification of the second outermost layer while the first outermostlayer, due to the high amount of bi-component fibers and theirresiliency will relatively expand more than the second outermost layer,thereby creating a density gradient from the wearer facing surfacetowards the garment facing surface of the absorbent structure. Thisgradient coincides with the same kind of gradient for capillarity whichis having the largest capillaries in the first layer, followed reducingcapillaries towards the second layer throughout the thickness of theabsorbent core. Both, the capillary as well as the density gradient areparticularly beneficial for the absorbent performance as liquid isdriven into the material and not released from it, but stored in thestorage core. This also has the surprising effect of providing anunsurpassed masking effect for the absorbent structure in that liquids,such as menstrual fluid or urine of older people having a rather strongyellowish color, will penetrate into the structure but be distributedwithin the structure, thereby displaying on the outer surface a reducedvisibly detectable stain size for the same kind of deposition whencompared with conventional structures or even the same combination oflayers but adhesively attached to each other.

As can be seen in FIG. 2, the region between one layer, in this Figureexemplified as layer (43) and a second layer, in this Figure simplifiedas layer (44), is a non-discreet transition zone (43.5). In thistransition zone, the materials from one layer have mixed with materialsfrom the adjacent layer. When combining the absorbent core in accordancewith the present invention, these transition zones, albeit extremelythin relative to the other layers, create an even stronger integrationbetween the layers of the absorbent core according to the presentinvention. Once integrated, the absorbent core structure cannot beseparated without destruction of this transition zone formed by theintegration of the absorbent core. Hence, when attempting to evaluatecores for compliance with the requirements of the present invention, itis necessary to use statistical means of separations in order to findreasonably accurate measurements of the quantities of materials in thevarious layers. One way of facilitating separation of layers in theabsorbent core according to the present invention is to use methods ofdeep-freezing, such as exposure to liquid nitrogen and cutting of thelayers under a microscope while the layers are in their frozen state.Such cuts have to be made in the center of the transition zones (43.5)as shown in FIG. 2.

The transition zones are technically important as they prevent stepchanges in characteristics such as capillarity, density,material-composition (due to material mixing). They are a result of theunitary formation of the cores. Many variations in the embodimentsaccording to the present invention are possible and are only limited bythe scope of the appended claims.

Backsheet

The absorbent article according to the present invention also comprisesa backsheet (50). The backsheet primarily has to prevent the extrudesabsorbed and contained in the absorbent structure from wetting materialsthat contact the absorbent article such as underpants, pants, pajamas,undergarments, and shirts or jackets, thereby acting as a barrier tofluid transport. In addition, however, the backsheet according to apreferred embodiment of the present invention permits the transfer of atleast water vapor, preferably both water vapor and air through it andthus allows the circulation of air into and water vapor out of thearticle. The backsheet typically extends across the whole of theabsorbent structure and can extend into and form part or all of sideflaps, side wrapping elements or wings, if present.

For a preferred embodiment according to the present invention suitablebreathable backsheet for use herein comprise at least one imperviouspolymeric backsheet layer such as a polyethylene film. The backsheet canalternatively comprise a resilient three-dimensional web, which consistsof a liquid impermeable film which has valve like apertures and isair/vapor permeable while retarding liquid transport. Preferredbreathable backsheet for use herein are those having a high vaporexchange, most preferably both a high vapor and high air exchange. Thefilm is oriented such that it retards or prevents liquid from passingfrom the absorbent core towards the outside due to the valve likeapertures while allowing free airflow through it.

In another embodiment an additional backsheet layer is provided togetherwith the above-mentioned aperture film. The additional layer is at leastwater vapor permeable so as to support breathability of the article. Itis not required but desirable that it also supports air permeability inorder to further improve the comfort benefit from the breathability ofthe article. In this context suitable water vapor and air permeablelayers include two-dimensional micro- or macro-aperture films, which canalso be micro- or macroscopically expended films, formed aperture filmsand monolithic films, as well as nonwovens, or wovens. Such films aredisclosed in detail e.g. in EPO 293 482 and the references therein, orU.S. Pat. No. 3,929,135, U.S. Pat. No. 4,637,819 and U.S. Pat. No.4,591,523. Preferably this film layer is made in accordance with theaforementioned U.S. Pat. No. 5,591,510 or PCT WO-97/03818, WO-97/03795.In particular, this layer comprises a polymeric film having capillaries.The preferred capillaries extend away from the wearer facing surface offilm at an angle that is less then 90 degrees. For ease of manufacturinga single layer or a recombined multi layer structure for use asbacksheet 50 is desirable.

Absorbent Article Construction

According to the present invention the elements of the article, thetopsheet, backsheet and absorbent core elements, are joined to eachother. The elements or layers are joined together across all or parts orportions of their common interface. In this manner the topsheet isjoined to the absorbent core, and the core is joined to the backsheet.Furthermore, if the backsheet comprises more than one layer, theselayers may also be similarly joined. In a particularly preferredembodiment the topsheet and backsheet extend beyond the periphery of theabsorbent core and the topsheet is directly (or indirectly) joined tothe backsheet to contain the absorbent core. In this context indirectlyjoining includes joining by means of an intermediate layer such as alayer of adhesive or another layer while direct joining includesadhesive joining by a distributed adhesive network or other meanscreating direct contact between layers, which are joined.

The elements of the article may be joined by any means known in the artfor affixing two adjacent layers of material, such that the layers aredirectly attached to one another or directly attached to one another viathe joining means. Suitable joining means include adhesive, fusionbonding, ultra sonic bonding, stitching, heat (e.g. thermo bonding bywelding fibers at intersections or melting a polymer to attach fibers orfilms to each other), embossing, crimping, pressure bonds, dynamicmechanical bonds or combinations thereof.

Especially if the absorbent article finds utility as a sanitary napkinor panty liner, the absorbent article is also provided with a pantyfastening means, which provides means to attach the article to anundergarment. For example the panty fastening means may comprise amechanical fastener such as hook and loop fasteners such as marketedunder the trade name VELCRO, snaps or holders. Alternatively, thearticle is fastened to the undergarment by means of panty fasteningadhesive on the backsheet. The panty fastening adhesive provides a meansfor securing the article to the panty and preferably a means forsecuring the article when soiled, to a fold and wrap package forconvenient disposal.

According to the present invention the absorbent article can be usedbeneficially in the context of sanitary napkins, panty liners,incontinence articles, sweat pads and diapers. However, sanitary napkinsand panty liners are particularly susceptible to the present invention.The disposable article may thus also have all those features and parts,which are typical for products in the context of their intended use. Forsanitary napkins this includes particularly wings or side flaps whichare provided on the side edges of the napkin and which fold around thecrotch edge of an undergarment. The side flaps can be provided asextensions of one or several of the elements of the napkin such as thetopsheet and/or backsheet. They can also be made separately and bejoined to the side margin of the napkin.

What is claimed is:
 1. Disposable absorbent article having a liquiddeposition region, said article comprising: a liquid pervious topsheetforming the outermost surface and wearer facing surface of said articleand consisting of a single layer at least in said liquid depositionregion, a backsheet forming the liquid barrier surface and garmentfacing surface of said article an absorbent core intermediate saidtopsheet and said backsheet, said core being unitary and having a wearerfacing and a garment facing surface, said garment facing surface beingimmediately adjacent said backsheet and said wearer facing surface beingimmediately adjacent said topsheet; said unitary core being a fibrous,stratified, layered structure of at least 3 layers in which all layersare unified into said unitary core, said core comprising a firstoutermost layer forming said wearer facing surface of said core, saidfirst layer is provided from a mixture of bi-component fibers andcellulose or viscose fibers, a second outermost layer forming saidgarment facing surface of said core, said second layer is provided bysoftener treated cellulose fibers having a weight fraction of theoverall core of 30%-50%, and at least one inner layer, sandwichedbetween said first and said second layer, said inner layer comprisingnon-softened cellulose fibers, optionally bi-component fibers, andfurther comprising super absorbent material.
 2. Disposable absorbentarticle according to claim 1, wherein said first outermost layer isprovided from a mixture of bi-component fibers and non-softenedcellulose fibers.
 3. Disposable absorbent article according to claim 1,wherein said first layer of said core comprises 60%-95% by weight ofbi-component fibers and 5%-40% by weight of cellulose or viscose fibers.4. Disposable absorbent article according to claim 1, wherein saidbi-component fibers in a cross section have a polypropylene centralportion and a polyethylene outer coating on said polypropylene. 5.Disposable absorbent article according to claim 4, wherein saidbi-component fibers are curled by having said central portion and saidouter coating non-symmetrically placed in respect to the center point ofthe cross section.
 6. Disposable absorbent article according to claim 1,wherein the bi-component fibers in said inner layer of said absorbentcore have a large diameter defined by a coarseness of at least 10 dtex.7. Disposable absorbent article according to claim 1, wherein all ofsaid bi-component fibers in the absorbent core are the same.